552 research outputs found
Evidence for postseismic deformation of the lower crust following the 2004 Mw6.0 Parkfield earthquake
Previous studies have shown that postseismic relaxation following the 2004 Mw6.0 Parkfield, CA, earthquake is dominated by afterslip. However, we show that some fraction of the afterslip inferred from kinematic inversion to have occurred immediately below the seismically ruptured area may in fact be a substitute for viscous postseismic deformation of the lower crust. Using continuous GPS and synthetic aperture radar interferometry, we estimate the relative contribution of shallow afterslip (at depth less than 20km) and deeper seated deformation required to account for observed postseismic surface displacements. Exploiting the possible separation in space and time of the time series of displacements predicted from viscoelastic relaxation, we devise a linear inversion scheme that allows inverting jointly for the contribution of afterslip and viscoelastic flow as a function of time. We find that a wide range of models involving variable amounts of viscoelastic deformation can fit the observations equally well provided that they allow some fraction of deep-seated deformation (at depth larger than âŒ20 km). These models require that the moment released by postseismic relaxation over 5 years following the earthquake reached nearly as much as 200% of the coseismic moment. All the models show a remarkable complementarity of coseismic and shallow afterslip distributions. Some significant deformation at lower crustal depth (20â26 km) is required to fit the geodetic data. The condition that postseismic deformation cannot exceed complete relaxation places a constraint on the amount of deep seated deformation. The analysis requires an effective viscosity of at least ~10^(18) Pa s of the lower crust (assuming a semi-infinite homogeneous viscous domain). This deep-seated deformation is consistent with the depth range of tremors which also show a transient postseismic response and could explain as much as 50% of the total postseismic geodetic moment (the remaining fraction being due to afterslip at depth shallower than 20 km). Lower crustal postseismic deformation could reflect a combination of localized ductile deformation and aseismic frictional sliding
Discrete-time synchronization of chaotic systems for secure communication
This paper deals with the problem of designing an exact nonlinear reconstructor for discrete-time chaotic encrypted messages. More precisely, we investigate the problem of designing a discrete-time dead-beat observer for nonlinear systems with unknown inputs. The application of the proposed observer in the context of secure communication and data transmission is also investigated
Grazing Analysis for Synchronization of chaotic hybrid systems
International audienceIn this paper, a Grazing bifurcation analysis is proposed and a way to chaos is presented. Moreover, based on this analysis an observer design for the synchronization of chaotic hybrid system is given
Nonlinear dynamic of the multicellular chopper
International audienceIn this paper, the dynamics of multicellular chopper are considered. The model is described by a continuous time three-dimensional autonomous system. Some basic dynamical properties such as Poincaré mapping, power spectrum and chaotic behaviors are studied. Analysis results show that this system has complex dynamics with some interesting characteristics
A canonical form for the design of unknown input sliding mode observers
International audienceIn this work, a new approach to solve the problem of designing an unknown input observer for linear systems is developed. An algorithm is given in order to find a suitable change of coordinates for the design of a step-by-step second order sliding mode observer. This observer provides, by usingthe equivalent output injections, a finite time estimation of both state and unknown inputs. Since the observer is based on second order sliding mode algorithms, the equivalent output injections are obtained in a continuous way without any use of low pass filters
State Observer and Observability Conditions for a Class of Hybrid Continuous-Discrete Dynamic System
International audienceThis paper deals with observability conditions and state observer design for a class of hybrid systems combining continuous and discrete dynamics. The main contribution of the work lies in the performed observability conditions for this class of systems and a design of hybrid observer to reconstruct both continuous and discrete states starting only from the knowledge of a continuous output. An illustrative example is presented showing the efficiency of the proposed observer
On sliding mode and adaptive observers design for multicell converter
International audienceIn this paper, a sliding mode and adaptive observers are proposed for multicell converter. The aim is to solve the problem of capacitor's voltages estimation by tacking account the hybrid behavior appearing in the multicell converters. Furthermore, an analysis of convergence for both observers is introduced. Finally some illustrative results of a 3-cell-converter are given in order to show the efficiency of the designed observers. The applicability of the designed observers are emphasized by the robustness test with respect to resistance load variation
Tire/Road Contact Condition Identification Using Algebraic Numerical Differentiation
International audienceIn this paper, a realistic simulation model for Wheeled Mobile Robot (WMR) is given by a dynamical system that switches between three models corresponding to three different tire/road contact conditions: ideal condition, skidding condition and slipping condition. Then, an algebraic based numerical identification for the discrete state (tire/road contact condition) of this switching system is proposed. Finally, specific estimators for the uncertain parameters encountered in the identification scheme are given
Geometrical Conditions for Output Depending Observability Normal Form
International audienceWe give geometrical conditions, which guarantee the existence of a diffeomorphism in order to transform a nonlinear system without inputs into a canonical normal form depending on its output. Moreover we extend our results to a class of systems with inputs. We end this paper by some examples and its simulations to highlight the proposed algorithm
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